The present invention relates to a position recognizing method and apparatus therefor, comprising the step of taking an image or an image taking means for recognizing the position of a position correcting mark mounted on a substrate constituting an electronic circuit or the position of parts such as an IC pad.
Recently, a position recognition is performed by a pattern such as an image in no contact with the position correcting mark mounted on a substrate constituting an electronic circuit or the position of a lead such as a QFP(quadrilateral flat package).
The conventional method for recognizing the position of an object is described below with reference to FIG. 4 showing the construction of the conventional pattern position recognizing apparatus. The apparatus comprises a positioning table 21; a lighting device 23 to be utilized in inputting the image of the pattern of an object 22 placed on the positioning table 21; a television camera 24 mounted on a movable television camera supporting section 25; and a television camera control circuit 26 for controlling the television camera 24.
A video signal inputted to the television camera 24 is outputted to an analog-to-digital converting circuit 27 in which analog signals are converted into digital signals, namely, image data of 0 to 255 (256 gray levels). Then, the data is inputted to a microcomputer comprising a CPU, ROM, RAM, and input/output ports.
The pattern position recognizing apparatus comprises a judge control circuit (CPU) 28 to which an instruction is transmitted from a main controller or an operation panel; a binary control circuit 29 for digitizing an input image; a window frame control circuit 30 for setting a range as a window frame so as to process the image; a partial template take-out circuit 31 for sequentially taking out a partial two-dimensional pattern from the binary image within the window frame; a target template memory circuit 32 for storing a pattern to be recognized as a target template in advance; a template comparing circuit 33 for comparing the stored target template with the target template stored in advance; a representative position detecting circuit 34 for detecting the position of a representative template determined by the template comparing circuit 33 as being the closest to the target template. The recognized result is transmitted to the main controller.
The operation of the apparatus of the above construction is described below.
As shown in FIG. 5 showing a flowchart, at step 21, the object 22 having a pattern to be recognized is placed on the positioning table 21 and the lens of the television camera 24 is focused on the object 22 to input the image thereof. At step 22, the inputted image is digitized. At step 23, a range to be processed is set as a window frame. At step 24, a partial template is taken out of a two-dimensional pattern inside the window frame. At step 25, the exclusive OR of the partial template is compared with that of each pixel (bit) of the target template so as to examine whether or not the partial template is approximately equal to the target template. At step 26, the operations of steps 24 and 25 are performed for all two-dimensional patterns within the window frame and the position of a recognized point at the upper left of the partial template which is maximum of all the sums of the exclusive OR is judged as the representative position of the partial template. If it is judged at step 27 that there is an error in the above operation at step 26, the program returns to step 21 at which an image input is performed and the subsequent operations are carried out by differentiating the level of digitization.
According to the above construction, the partial template taken out of the two-dimensional pattern is compared with the sum of the exclusive OR of each pixel (bit) of the two-dimensional target template to check whether or not the partial template is approximately equal to the target template. Therefore, it takes a very long time to process data because of the large amount of data.
A position recognition is carried out with a low accuracy if a digitation is performed at the same level. This is because of density fluctuation caused by an illuminance change which may occur at the time of the image input or the sensitivity change of the television camera. As a result, the process for controlling the level of the digitization is complicated and the period of time required therefor is long.
Further, it is very difficult to recognize the position of a pattern such as a gold mark, placed on a ceramic substrate for use in an electronic circuit substrate, which does not uniformly glitter.